Titania particles and a process for their production

ABSTRACT

The invention provides a process for the production of titania particles with a desired morphology. The process comprises providing a titania sol and then drying the sol to provide dried titania particles. The process is characterized in that the morphology of the dried titania particles is controlled by applying one or more of the following criteria: (a) the titania sol is produced from a TiO2 containing slurry obtained using a precipitation step in a sulphate process, wherein the size of micelles formed during the precipitation is controlled; (b) the titania sol is produced from a TiO2 containing slurry and the pH of the slurry is controlled in order to affect the extent to which the titania sol is flocculated; (c) the titania sol is produced from a TiO2 containing slurry and the iso-electric point of the titania is adjusted in order to affect the extent to which the titania sol is flocculated; (d) the titania sol is dried by application of heat and the temperature used during the drying step is controlled.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of International ApplicationPCT/GB2014/052878 filed Sep. 22, 2014 which designated the U.S. andwhich claims priority to Great Britain App. Serial No. 1316874.5 filedSep. 23, 2013 and Great Britain App. Serial No. 1415175.7 filed Aug. 27,2014. The noted applications are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates, in general, to titania particles and to processesfor their production and use.

BACKGROUND TO THE INVENTION

Titanium dioxide (titania) is well known and has a variety ofapplications, including cosmetics, personal care products, plastics,surface coatings, self-cleaning surfaces, drug delivery and medicaldevices, as a catalytic carrier material and in photovoltaicapplications.

There are two main processes for making raw titanium dioxide: thesulfate process and the chloride process.

The sulfate process is based on the digestion of ilmenite or titaniaslag in concentrated sulfuric acid. After iron removal as iron sulfate,the solution is heated and diluted with water. The titanium hydrolyzes,forming a titanium oxysulfate precipitate, which is further treated toproduce TiO₂ pigment.

The chloride process relies on carbochlorination of titanium containingore or intermediate products to form TiCl₄, followed by the gas phaseoxidation of TiCl₄.

Titanium dioxide can be flocculated and/or precipitated out of a slurrycontaining titanium dioxide by pH adjustment of the slurry.

The finishing process for titanium dioxide, as obtained by any knownmethod, may include one or more of: drying, milling, filtering, washing,and packaging.

Many applications require the titania to have a large specific surfacearea (e.g. greater than 200 m²/g), in order to increase efficacy. Inparticular this is due to the fact that such larger surface areas resultin increased gas to solid contact ratios or increased liquid to solidcontact ratios. Such large specific surface areas can be achieved by theuse of nano particles of titania (i.e. particles with a diameter of lessthan 100 nm) and this is the current normal approach.

However, the use of nano materials has attracted publicity and concernsfrom some areas. In general, there has been much debate generated withregard to the environmental health and safety implications of nanomaterials.

There can also be applications where control of the surfacearea/porosity to be within certain ranges can be desired; the largestpossible specific surface area is not always what is required.

There is also a desire for titania material that has a particle shapesuited to the desired end use of the material. Dependent on the intendeduse, different shapes of particles may be more appropriate.

Thus it has been identified by the inventors that there is a clear needfor methods that permit control of morphology (i.e. form and structure)when manufacturing titania particles. The morphology may in particularrelate to the pore size in the titania particles (which in turn impactson the specific surface area of the particles) and/or the shape of thetitania particles (e.g. in terms of whether the particles are sphericalin shape or present an alternative shape such as a toroid (i.e. adoughnut-type shape), and whether the particles are “fluffy” or have asmooth surface).

In this regard, it is particularly desired to be able to controlporosity (and thus specific surface area) when manufacturing titaniaparticles and/or to control particle shape when manufacturing titaniaparticles, in order that particles having a suitable porosity and/orshape for the desired application can be prepared.

SUMMARY OF THE INVENTION

The invention provides, in a first aspect, a process for the productionof titania particles with a desired morphology, the process comprising:

-   -   providing a titania sol;        and then    -   drying the sol to provide dried titania particles;        characterised in that the morphology of the dried titania        particles is controlled by applying one or more of the following        criteria:    -   (a) the titania sol is produced from a TiO₂ containing slurry        obtained using a precipitation step in a sulphate process, and        the size of micelles formed during the precipitation is        controlled,    -   (b) the titania sol is produced from a TiO₂ containing slurry        and the pH of the slurry is controlled in order to affect the        extent to which the titania sol is flocculated,    -   (c) the titania sol is produced from a TiO₂ containing slurry        and the iso-electric point of the titania is adjusted in order        to affect the extent to which the titania sol is flocculated;    -   (d) the titania sol is dried by application of heat and the        temperature used during the drying step is controlled.

In this regard, the morphology refers to the form and structure of thetitania particles. The morphology includes, but is not limited to, thesize of pores in the titania particles (which in turn impacts on thespecific surface area of the particles) and the shape of the titaniaparticles.

The invention provides, in one such aspect, a process for the productionof titania particles with a desired morphology, the process comprising:

-   -   providing a titania sol;        and then    -   drying the sol to provide dried titania particles;        characterised in that:        (A) the pore size of the dried titania particles is controlled        by applying one or more of the following criteria:    -   (A-i) the titania sol is produced from TiO₂ containing slurry        obtained using a precipitation step in a sulphate process, and        the size of micelles formed during the precipitation is        controlled,    -   (A-ii) the titania sol is produced from a TiO₂ containing slurry        and the pH of the slurry is controlled in order to affect the        extent to which the titania sol is flocculated,    -   (A-iii) the titania sol is produced from a TiO₂ containing        slurry and the iso-electric point of the titania is adjusted in        order to affect the extent to which the titania sol is        flocculated;        and/or        (B) the shape of the dried titania particles is controlled by        applying one or more of the following criteria:    -   (B-i) the titania sol is produced from a TiO₂ containing slurry        and the pH of the slurry is controlled in order to affect the        extent to which the titania sol is flocculated,    -   (B-ii) the titania sol is dried by application of heat and the        temperature used during the drying step is controlled.

The invention also provides, in a second aspect, the use of a controllednucleation during preparation of a titania sol by a precipitation stepin a sulphate process, before then drying said sol, wherein the size ofmicelles formed during the precipitation is controlled so as to controlthe morphology of the resultant dried titania particles. Preferably, theprecipitation is controlled so as to control the pore size and/orspecific surface area of the resultant dried titania particles.

The invention also provides, in a third aspect, the use of a controlledflocculation during preparation of a titania sol from a titania slurry,before then drying said sol, wherein the extent to which the sol isflocculated is controlled by adjusting the pH of the slurry, so as tocontrol the morphology of the resultant dried titania particles.Preferably, the flocculation is controlled so as to control the poresize and/or specific surface area and/or particle shape of the resultantdried titania particles. The pH may be adjusted to be closer to theiso-electric point of the titania, so there is a greater degree offlocculation, or the pH may be adjusted to be further from theiso-electric point of the titania, so there is a lesser degree offlocculation.

The invention also provides, in a fourth aspect, the use of a controlledflocculation during or after the formation of a titania sol, before thendrying said sol, wherein the extent to which the sol is flocculated iscontrolled by adjusting the iso-electric point of the titania, so as tocontrol the morphology of the resultant dried titania particles.Preferably, the flocculation is controlled so as to control the poresize and/or specific surface area of the resultant dried titaniaparticles. The iso-electric point may be adjusted so as to be closer tothe pH of the slurry/sol, so there is a greater degree of flocculation,or the iso-electric point may be adjusted to be further from the pH ofthe slurry/sol, so there is a lesser degree of flocculation.

The invention also provides, in a fifth aspect, the use of a controlleddrying during preparation of dried titania particles from a titania sol,wherein the temperature used during the drying step is controlled so asto control the morphology of the resultant dried titania particles.Preferably, the temperature is controlled so as to control the particleshape of the resultant dried titania particles.

The invention therefore permits the formation of titania with desiredmorphology, e.g. in terms of desired pore size and/or desired particleshape. The invention may be practised on titania with a range ofparticle sizes, including nano, meso and macro particles.

It may, for example, be used to provide titania with large specificsurface areas but which can be used in applications where there is adesire to avoid the need to use nano materials.

In a sixth aspect of the invention, a process for producing titaniacomprises:

-   -   providing a titania sol;        and then    -   spray drying the sol to provide dried titania particles;        characterised in that the morphology of the dried titania        particles is controlled by:    -   (i) the titania sol being produced from a TiO₂ containing slurry        and the pH of the slurry being controlled to be 3 pH units or        more from the iso-electric point of the titania, by the addition        of peptising agent, in order to reduce the extent to which the        titania sol is flocculated; or    -   (ii) the titania sol being produced from a TiO₂ containing        slurry and the iso-electric point being adjusted to be 3 pH        units or more from the pH of the slurry, by the addition of        dispersant, in order to reduce the extent to which the titania        sol is flocculated.

This process is beneficial in that by controlling the pH duringpeptisation to be away from the iso-electric point (which will normallybe at about pH 5-6), or by adjusting the iso-electric point to be awayfrom the pH of the slurry, the sol will be fully dispersed (notflocculated). Following this with a spray drying treatment results in aparticulate product that has a smooth curved outer surface, that isrelatively small in size (particle diameter of 30 μm or less), and thathas high integrity, being resistant to external forces including highshear mixing. The particles may be spherical or toroidal but have acontinuous exterior curved (convex) surface.

In one embodiment, the pH of the slurry is adjusted to be 3.5 pH unitsor more, or 4 pH units or more, such as from 4 to 6 pH units, away fromthe iso-electric point of the titania, by the addition of peptisingagent, in order to reduce the extent to which the titania sol isflocculated. The pH of the slurry is adjusted by the addition of anysuitable peptising agent (examples of which are set out below). Onesuitable peptising agent is a monoprotic acid, such as hydrochloricacid, which will lower the pH and take it away from the iso-electricpoint.

In one embodiment, the iso-electric point of the titania is adjusted tobe 3.5 pH units or more, or 4 pH units or more, such as from 4 to 6 pHunits, away from the pH of the slurry, by the addition of a dispersant,in order to reduce the extent to which the titania sol is flocculated.The iso-electric point of the titania is adjusted by the addition of anysuitable dispersant (examples of which are set out below). One suitabledispersant is an α-hydroxy carboxylic acid, such as citric acid.

In one embodiment, the process comprises:

-   -   providing a titania sol;        and then    -   spray drying the sol to provide dried titania particles;        characterised in that the morphology of the dried titania        particles is controlled by:    -   the titania sol being produced from a TiO₂ containing slurry and        the pH of the slurry being controlled to be in the range of from        1 to 3, by the addition of peptising agent, in order to the        reduce the extent to which the titania sol is flocculated.

This process is beneficial in that by controlling the pH duringpeptisation to be low the sol will be fully dispersed (not flocculated).Following this with a spray drying treatment results in a particulateproduct that has a smooth curved outer surface, that is relatively smallin size (particle diameter of 30 μm or less), and that has highintegrity, being resistant to external forces including high shearmixing. The particles may be spherical or toroidal but have a continuousexterior curved (convex) surface.

In a preferred embodiment, the pH of the slurry is controlled to be inthe range of from 1 to 2, especially from 1 to 1.5, by the addition ofpeptising agent, in order to the reduce/minimise the extent to which thetitania sol is flocculated.

Although any peptising agent may be used, in one embodiment the pH ofthe slurry is controlled by the addition of hydrochloric acid, oranother monoprotic acid, as peptising agent.

In the process of the sixth aspect, it may be that after the addition ofdispersant/the addition of peptising agent, the sol is then neutralised(e.g. with monoisopropanolamine—known as MIPA). Excess soluble salts maybe removed to a desired conductivity, e.g. using cross-flow filtration,for example the washing may reduce the conductivity to <2 ms/cm.

It may be that the morphology of the dried titania particles is furthercontrolled by the temperature used during the spray drying step beingcontrolled; in one such embodiment the temperature of spray drying iscontrolled to be in the range of from 50 to 150° C., such as from 75 to140° C., or from 100 to 125° C. This further assists in the productionof small strong particles, which are preferably spherical.

The sol as spray dried may in one embodiment have a solids content offrom 1% to 35% wt/wt, e.g. from 2 to 25% wt/wt or from 5 to 20% wt/wt orfrom 10 to 18% wt/wt.

It may be that the morphology of the dried titania particles is furthercontrolled by the titania sol being produced from a TiO₂ containingslurry obtained using a precipitation step in a sulphate process,wherein the size of micelles formed during the precipitation iscontrolled to be in the range of 10 to 150 nm, such as from 15 to 125nm, or from 20 to 100 nm.

It may be suitably that the size of micelles formed during theprecipitation is controlled to be in the range of from 20 to 50 nm. Forexample, in one embodiment they may be sized from 20 to 45 nm or from 20to 40 nm or from 25 to 45 nm or from 25 to 40 nm.

In one such embodiment the size of micelles formed during theprecipitation is controlled by the use of a Mecklenburg precipitationwith a nucleation level in the range of from 0.1 to 15 wt %, e.g. offrom 1 to 15 wt %, or from 5 to 12 wt %.

It may be suitably that the nucleation level is from 5 to 10 wt %, suchas from 5.5 to 9 wt %, and especially in the range of from 6 to 8 wt %.

In another such embodiment the size of micelles formed during theprecipitation is controlled by the use of a Blumenfeld precipitationwith a drop ratio of from 50:50 to 99:1, e.g. from 50:50 to 80:20 orfrom 50:50 to 78:22 or from 50:50 to 75:25 (such as from 60:40 to 75:25)or from 80:20 to 98:2 or from 82:18 to 98:2 (such as from 85:15 to98:2).

It may suitably be that the drop ratio is in the range of from 50:50 to75:25 or from 50:50 to 70:30, e.g. from 55:45 to 75:25, such as from60:40 to 75:25 or from 55:45 to 70:30.

Therefore the invention also provides, in a seventh aspect, titania inthe form of particles that are obtainable by the process of the sixthaspect of the invention.

In particular, these particles as obtainable by this process each have acontinuous exterior convex surface, the particles having a diameter, asmeasured by using laser diffraction, of 30 μm or less, and a BETspecific surface area of 50 m²/g or more, wherein the particles areporous.

Preferably the particles are spherical in shape or toroidal in shape.

Preferably the particles have a diameter, as measured by using laserdiffraction, of 20 μm or less, such as from 2 to 20 μm.

Preferably the particles have a BET specific surface area of 80 m²/g ormore, such as from 80 to 320 m²/g.

The particles of the seventh aspect are beneficial in that they havehigh integrity, being resistant to external forces, including high shearmixing. This high integrity is preserved even after heat treatment (e.g.after being thermally treated at 500° C. for 7 days), as is shown in theexamples.

Therefore these novel particles have the ability to retain their sizeand shape even when exposed to a high level of external force.

These novel particles may, in an eighth aspect, be used as a catalyst oras a catalytic support. They may in particular be used as a catalyst oras a catalytic support where that catalyst or catalytic support isproduced by a method that involves exposure to external forces, e.g.extrusion or high shear mixing.

In this regard, it may be that the porous titania of the seventh aspectis mixed with a binder and extruded to create high surface area titaniapellets for use as a catalyst or catalyst support. If the titania is tobe used as a support, it may be a support for any catalytic material.The catalytic material may, however, suitably be selected from the groupconsisting of: ruthenium, rhodium, palladium, iridium, platinum, osmium,iron, cobalt, nickel, copper, silver, vanadium, tungsten, chromium andmolybdenum, and combinations thereof.

In one embodiment, the titania may be coated with silica or the like toprovide improved thermal stability.

In one embodiment, the porous titania particles or extrudate formedtherefrom may undergo an impregnation process, whereby catalyticpromoters (such as molybdenum, nickel, cobalt, or a mixture thereof) areimpregnated into the pores of the porous titania.

In one embodiment, a thermal stabiliser (such as tungsten trioxide froma precursor such as ammonium metatungstate or ammonium paratungstate,lanthanum oxide from a precursor such as lanthanum nitrate hexahydrate,cerium oxide from a precursor such as cerium nitrate hexahydrate, orsilica from a precursor such as silicic acid) is incorporated. This canact to improve catalyst performance by maintaining a high BET surfacearea at elevated temperatures.

In one preferred embodiment the titania particles of the seventh aspect(or an extrudate formed therefrom) are used as a catalyst or as acatalytic support in an application selected from the group consistingof: emissions catalysis; catalysis of industrial chemical reactions; andphotocatalysis. In one embodiment the particles (or an extrudate formedtherefrom) are used as a catalyst or as a catalytic support in anapplication selected from the group consisting of: selective catalyticreduction of nitrogen-based gases (including in combined diesel particlefilter/selective catalytic reduction units); desulphurisation of gasesin the petroleum industry by the Claus process; and photocatalyticcleaning, purification or disinfection.

It is particularly beneficial to use the particles in emissionscatalysis and especially selective catalytic reduction (SCR). There aretwo main manufacturing processes used in relation to SCR: i) an extrudedceramic product is prepared, which is made from a carrier based ontitania, alumina and/or zeolites, with the active catalysts being mixedinto the carrier prior to extruding; and ii) a ceramic or metal productis prepared, which is then dipped into a slurry containing titania andactive catalysts, which is then dried; this is known as a washcoat. Ineither case the product has a “honeycomb” form.

Good strength properties and robustness may be particularly importantwhen titania particles are used in an SCR manufacturing process thatuses an extrusion processes.

Therefore in one embodiment the novel particles of the seventh aspectare extruded under high pressure, through extrusion dies, to produce acatalytic product suitable for use in exhaust systems.

One or more active catalysts are mixed into the carrier prior toextruding. Active catalysts may suitably be selected from the groupconsisting of: ruthenium, rhodium, palladium, iridium, platinum, osmium,iron, cobalt, nickel, copper, silver, vanadium, tungsten, chromium andmolybdenum, and combinations thereof. In the field of emissionscatalysts, platinum, palladium, tungsten and/or vanadium tend to bepreferred. In one embodiment, the catalyst is platinum and/or vanadium.

The novel particles of the seventh aspect may be mixed with any otherdesired materials (e.g. other carrier or support materials, or bindermaterials), before extrusion. In one embodiment, the particles may bemixed with a cordierite and a binder as well as with active catalystmaterial before then being extruded to form a catalyst product.

The strength characteristics of the novel particles of the seventhaspect mean that they are less likely to collapse under external forces,e.g. high pressures. Therefore they retain their shape, size andporosity characteristics. Known porous products may, in contrast, befound to exhibit some degree of collapse or reduction in pore size underpressure.

Accordingly, in a ninth aspect of the invention, a process for preparinga catalyst product is provided, the process comprising the steps of:

-   -   providing dried titania particles according to the seventh        aspect;    -   mixing the particles with active catalyst material;    -   extruding the mixture under pressure, through extrusion dies, to        produce a catalyst product.

The active catalyst material may be one or more active catalysts,preferably selected from those discussed above in relation to the eighthaspect.

In one embodiment, the process also includes the step of mixing theparticles with other carrier or support materials (e.g. ceramics, suchas alumina or cordierite, or zeolites) and/or binder materials. This maybe carried out before or after the step of mixing the particles withactive catalyst material, but must be carried out before the extrusionstep.

In one embodiment, the step of providing dried titania particlesaccording to the seventh aspect is carried out by carrying out theprocess of the sixth aspect.

The catalyst product made by the process of the ninth aspect isparticularly suitable for use in exhaust systems. Due to the improvedrobustness of the titania particles in the product, the catalyst producthas improved catalytic properties, because the titania particles retaintheir porosity even after the extrusion process involved in themanufacturing process. As will be appreciated by the skilled reader,improved porosity for the carrier/support is influential on theproperties of a catalyst product.

In a tenth aspect, therefore, there is provided a catalyst productcomprising titania and catalyst material, the catalyst product beingobtainable by the process of the ninth aspect.

DETAILED DESCRIPTION OF THE INVENTION

The present invention permits the control of the morphology of titaniaparticles, both in terms of the overall shape of the particles (e.g.spherical or toroidal, smooth outer surface or rough outer surface,dense or hollow) and in terms of pore size (which in turn will impact onthe specific surface area).

Although the present invention can be applied to titania particles ofany size, as noted above there are issues surrounding use of nanomaterials in some areas and there is a desire for an alternative titaniamaterial that has a large specific surface area. Accordingly, in someembodiments the titania particles may be sized so as to be larger thannanoparticles, e.g. they may be meso or macro particles. In someembodiments the titania particles may have a particle size of greaterthan 0.1 μm.

The titania particles of the invention may suitably have a particle sizeof greater than 0.15 μm, e.g. of 0.2 μm or more, 0.3 μm or more, 0.4 μmor more, 0.5 μm or more, 0.6 μm or more, 0.7 μm or more, 0.8 μm or more,or 0.9 μm or more. In some embodiments the particle size is 1.0 μm ormore, such as 1.1 μm or more, 1.2 μm or more, 1.3 μm or more, 1.4 μm ormore, 1.5 μm or more, 1.6 μm or more, 1.7 μm or more, 1.8 μm or more, or1.9 μm or more. The particle size may be 2.0 μm or more.

In some embodiments the titania particles may have a particle size offrom 0.2 μm to 15 μm, such as from 0.5 μm to 12 μm, e.g. from 0.7 μm to10 μm or from 0.8 μm to 8 μm, such as from 1 μm to 6 μm or from 1.5 μmto Slim or from 2 μm to 4 μm.

The particle size is a geometric weight mean value for the particle size(appropriate for the approximately log normal distribution which isoften found with such particles).

The particle size may alternatively be determined by laser diffractionand may be measured using a laser diffraction machine, such as thoseavailable from Malvern Instruments Ltd, e.g. a MasterSizer machine.

The particle size may alternatively be determined by X-ray sedimentationand may be measured using a X-ray disc centrifuge, such as thoseavailable from Brookhaven, e.g. a BI-XDC machine.

As one skilled in the art is aware, crystal size is distinct fromparticle size. Crystal size relates to the size of the fundamentalcrystal units having internally consistent lattice planes, which make upthe particulate material. Conventional manufacturing processes thatmanufacture titanium dioxide as a pigment will generate crystallitesduring a precipitation process; these are considered fundamentalparticles and are generally accepted to be in the order of 100 Å. Duringthe precipitation process, the crystallites self-assemble into “rafts”known as micelles. These are lenticular in shape and generally have anaspect ratio of about 3:1, having a major axis of about 350 Å for rutileand about 600 Å for anatase. Conventional manufacturing processes thatmanufacture titanium dioxide as a pigment will incorporate a thermalprocessing step that causes the crystal centres of these crystallites tocombine and create much larger crystals.

For example, conventional titanium dioxide product in a rutile crystalform has a crystal size of about 0.17 μm-0.29 μm and a particle size ofabout 0.25 μm-0.40 μm while conventional titanium dioxide product in ananatase crystal form has a crystal size of about 0.10 μm-0.25 μm and aparticle size of about 0.20 μm-0.40 μm. The particle size is thusaffected by factors such as the crystal size and incomplete fusion ofcrystals—as well as milling techniques used during production, such asdry, wet or incorporative milling, and subsequent treatments that causeaggregation of crystals.

The crystal size and particle size of the titanium dioxide may bedetermined by methods well known to those skilled in the art. Forexample, the crystal size may be determined by transmission electronmicroscopy on a rubbed out sample with image analysis of the resultingphotograph. The results of the crystal size may further be validated byreference using latex NANOSHPHERE™ Size Standards (available from ThermoScientific). As noted above, a method which may be used for determiningthe particle size of the titanium dioxide is laser diffraction. X-raysedimentation may be used as an alternative.

The particle size of the titanium dioxide may therefore be greater thanor about equal to the crystal size.

In general, to produce titanium dioxide, natural ores (such as ilmeniteand mineral rutile), enriched ores (such as titanium slag andbeneficiated ilmenite), or mixtures thereof may be used as the startingraw material. These ores may be processed by any suitable means, such asthe sulphate process or the chloride process, to produce titaniumdioxide crystallites and micelles of a required purity and size. This isknown in the art and is conventional. It will be appreciated that thetitanium dioxide as provided in sol form in the process of the inventioncan, on the whole, be obtained by any suitable technique and theinvention is not limited to any method of manufacture. However, it maybe preferred to use the sulphate process as this then permits the use ofa controlled nucleation during preparation of the titania sol by aMecklenburg, Blumenfeld or other precipitation step in this sulphateprocess.

One or more of the conditions discussed above may be controlled in orderto select the pore diameters of the titania particles (i.e. the actualpores within the particles themselves, as compared to the packingbetween particles or the pores within the micelles that make up theparticles). Preferably, the titania particles of the invention may havepore diameters which are greater than 2 nm.

In one embodiment, the titania particles are mesoporous, having porediameters which are greater than 2 nm but less than 50 nm, e.g. from 3nm to 45 nm or from 5 nm to 40 nm.

In other embodiments, the titania particles are macroporous, having porediameters which are 50 nm or greater, e.g. from 50 nm up to 1000 nm orfrom 50 nm to 500 nm.

It may be desired to control the pore diameters to be from 4 nm to 50nm, e.g. from 5 nm to 50 nm or from 10 nm to 50 nm, such as from 20 nmto 45 nm or from 25 nm to 40 nm.

Pore diameter may be measured using mercury porosimetry (for a porediameter range of about 3 nm up to 200 μm), e.g. using a MicromeriticsAutoPore IV porosimeter, and/or by nitrogen isotherms (for porediameters in the nanometer range), e.g. using a Micromeritics TriStar3020™ machine.

One or more of the conditions discussed above may be controlled in orderto select the specific surface area of the titania particles.Preferably, the titania particles of the invention may have a specificsurface area which is greater than 100 m²/g.

The titania particles of the invention may have a specific surface areaof greater than 125 m²/g, e.g. of 150 m²/g or higher or 175 m²/g orhigher. In one embodiment, they have a specific surface area of 200 m²/gor higher, such as 210 m²/g or higher, or 220 m²/g or higher, or 225m²/g or higher.

In one embodiment, they have a specific surface area of 230 m²/g orhigher, such as 235 m²/g or higher, or 245 m²/g or higher or 250 m²/g orhigher. It may be that the titania particles have a specific surfacearea of 260 m²/g or higher, or 270 m²/g or higher, or 275 m²/g orhigher, or 280 m²/g or higher, or 290 m²/g or higher. It may even bethat the titania particles of the invention have a specific surface areaof greater than 300 m²/g.

There is no particular upper limit to the specific surface area for thetitania particles of the invention, but in one embodiment it is up to350 m²/g, or up to 400 m²/g, or up to 450 m²/g, or up to 500 m²/g. Thismay for example, apply in an embodiment where the crystal size is aboutis 4 nm.

The specific surface area may be determined using the Brunauer, Emmettand Teller method (BET method) as described in J. Am. Chem. Soc., 1938,60, 309.

One or more of the conditions discussed above may be controlled in orderto control the shapes of the titania particles. It may be that thetitania particles of the invention have shapes that are spherical, or itmay be that the shapes are ellipsoids (e.g. a prolate (elongated)spheroid or an oblate (flattened) spheroid), or it may be that theshapes are toroidal (doughnut-shaped), or they may appear cotton-woollike or fluffy. It may be that the titania particles of the inventionhave smooth outer surfaces or the outer surfaces may be rough. It may bethat the titania particles of the invention are dense or they may behollow.

The processes provided for forming the titania particles firstly involvethe provision of a titania sol. A titania sol is a colloidal suspensionof TiO₂ particles. The TiO₂ particles used may be anatase, rutile oramorphous or a mixture thereof.

As will be well understood by the skilled person, a sol is a colloidalsuspension of solid particles in a liquid. In this regard, a colloid isa suspension of particles whereby the particle size is small enough soas not to be affected by gravitational forces and so the particlesremain suspended over an extended period of time under standardconditions, e.g. for a day or more, a week or more, or a month or more(such as a year or more) at room temperature and pressure.

The liquid in which the titanium dioxide particles are provided ispreferably polar. In one embodiment, the liquid is aqueous; this may bewater or an aqueous solution. However other polar carriers for theparticles could also be contemplated, e.g. they may be selected frompolar organic solvents or alcohols. The liquid carrier may also be amixture of two or more polar carriers, e.g., it may be a mixture ofwater and alcohol.

The titania particles in the titania sol may be derived from anysuitable precursor. In one embodiment, they are derived from a titaniumdioxide obtained from a sulphate manufacturing process (e.g. aMecklenburg or Blumenfeld precipitation). They may, in one embodiment,be derived from a titanium dioxide obtained from a titanium oxysulphateprecursor.

In one embodiment, the titania sol is produced from TiO₂ prepared by aprecipitation step in a sulphate process (e.g. a Mecklenburg orBlumenfeld precipitation).

After precipitation, the obtained titania hydrate may be filtered,washed free of impurities, and contacted with an aqueous base to form asuspension having a pH of about neutral.

Sulphate ions can then be removed from the neutralized suspension byfiltration and washing. It may be that the filter cake obtained afterfiltration is washed until the SO₄ ²⁻ content of the wash filtrate isless than 0.1 g/l (which may be determined by barium chloride solutiontitration).

The filter cake is then slurried in water to produce an aqueoussuspension of titania hydrate. This can then be peptized with acid pHadjustment (e.g. with a strong monoprotic acid pH adjustment) to providethe nano titania sol.

In one preferred embodiment, the titania sol that is provided is aconcentrated, neutral titania sol made in accordance with the processdescribed in WO2011/033286.

In one embodiment the titania sol that is provided has been obtained bypreparing a pulp via a sulphate process (e.g. with a Mecklenburg orBlumenfeld precipitation). Said pulp is then neutralised (e.g. withaqueous ammonia). Optionally, the material is washed free fromsulphates. The slurry is then peptised (e.g. using hydrochloric acid).

Optionally, the iso-electric point of the titania is lowered (e.g. withthe addition of citric acid). The slurry may then be neutralised (e.g.with monoisopropanolamine).

Excess soluble salts may then be removed to a desired conductivity, e.g.using cross-flow filtration, followed by water removal to concentratethe sol.

It will be appreciated that the present invention is based around theability to control the pore size in the particles and the ability tocontrol the shape of the particles, to obtain a particulate product thathas characteristics suitable for a given end use. The factors to becontrolled in the present invention are described in more detail below:

Controlled Nucleation During Preparation of a Titania Sol by a SulphatePrecipitation Step

As the skilled person will appreciate, micelles are the fundamentalstructural units of titania manufactured from the sulphate process.During the sulphate process crystallites precipitate out from a titaniumand sulphuric acid solution; these are of the order of 100 Å indiameter. The micelles are then formed by these crystallites being boundtogether by sulphate ions and water; usually these stable micelles areformed from hundreds of crystallites. The micelles are lenticular inshape and the major axis is usually sized of the order of 600 Å.

The size of the micelles created at precipitation may be controlled byvarying the level of nuclei used in the process for preparing the sol.As the skilled person will understand, in the Mecklenburg processnucleation involves seeding the sol during precipitation with nuclei,which are finely sized titania particles, to initiate or enhance crystalgrowth. In the Blumenfeld process, self nucleation occurs, and theconditions are controlled to impact the extent of self nucleation. Otherprecipitation methods are also known and during these precipitationmethods the size of the micelles can likewise be controlled.

It is generally accepted that each micelle contains one nucleus and thatthe number of micelles remains constant during precipitation. In theMecklenburg process, the number of micelles is a function of the numberof nucleating sites introduced. As TiO₂ is precipitated, the ultimatesize of the micelle is therefore also a function of the number ofnucleating sites: the more nucleating sites available, the smaller thefinal micelles. These micelle particles will then flocculate intolarger, less well defined particles in a standard precipitation; theseare generally in the order of up to ˜2 μm in a standard sulphate processprecipitation.

In the Blumenfeld process, the nucleating sites develop spontaneously;aqueous TiOSO₄ (referenced as the “TiOSO₄-containing liquor”) isintroduced at a carefully controlled rate into a volume of water(referenced as the “foot water”) that is initially large in volume incomparison with the volume of the added TiOSO₄ solution(TiOSO₄-containing liquor). At this point, there is initially a highwater concentration, which drives the reactionTiOSO₄+nuclei+OH⁻→TiO₂ nH₂O+H₂SO₄to the right and so promotes the nucleation of anatase. As furtheraddition of aqueous TiOSO₄ continues, hydrolysis of TiO₂ is stopped dueto increasing acid concentration; and the reaction is then driven to theleft. When all the aqueous TiOSO₄ has been introduced, there will besufficient nuclei to continue the precipitation.

Two variables influence the number of nucleating sites; these are:

-   -   i) The ratio of the volume of the TiOSO₄-containing liquor to        the foot water, known as the ‘drop ratio’.    -   ii) The time taken to completely introduce the required volume        of the TiOSO₄ containing liquor to the foot water, known as the        ‘drop time’.

In the present invention, it has been determined that by controlling thedrop ratio it is possible to grow micelles in a Blumenfeld precipitationin the same size range as that of a Mecklenburg precipitation (wherenuclei level can be changed by changing the volume of nuclei added).

Where a process is used other than Mecklenburg or Blumenfeld, theprocess should be analysed to determine if nuclei are created in situ orex situ. Where nucleation is ex situ, smaller pores will result from useof greater quantities of nuclei. Where nucleation is in situ, thereaction time may be shortened or the dilution increased, to reduce poresize.

In one preferred embodiment, the nano titania sol that is provided isone where the precipitated titania micelles have been controlled so asto be sized from 10 to 150 nm or more, (e.g. from 10 to 200 nm) such asfrom 15 to 125 nm, or from 20 to 100 nm. In one such embodiment, thenano titania sol that is provided is one where the precipitated titaniamicelles have been controlled so as to be sized from 10 to 60 nm, suchas from 15 to 55 nm, and preferably from 20 to 50 nm. For example, theymay be sized from 20 to 45 nm or from 20 to 40 nm or from 25 to 45 nm orfrom 25 to 40 nm.

The larger the micelles, the higher the pore size in the resultanttitania particles.

Micelle size can be controlled in the Mecklenburg process by controllingthe nucleation level. In this regard, a lower level of nuclei giveslarger micelles.

In one embodiment, the sol is prepared with a nucleation level of 0.1 wt% or higher, such as 0.5 wt % or higher. In one embodiment, the sol isprepared with a nucleation level of 15 wt % or less. In one embodiment,the sol is prepared with a nucleation level of from 1 to 15 wt %.

By controlling the nucleation level to be at the lower end of the range,e.g. from 0.1 to 5 wt %, or from 0.3 to 4.5 wt %, or from 0.5 to 4 wt %,or from 0.7 to 3.5 wt %, or from 1 to 3 wt %, larger micelles areobtained and thus a higher pore size (diameter).

By controlling the nucleation level to be at the higher end of therange, e.g. from 5 to 15 wt %, or from 5 to 12 wt %, or from 5.5 to 10wt %, or from 6 to 8 wt %, smaller micelles are obtained and thus asmaller pore size (diameter).

As noted above, micelle size can be controlled in the Blumenfeld processby varying the drop ratio. An increased drop ratio gives largermicelles.

In one embodiment, the sol is prepared using a drop ratio (ratio ofliquor to water used by volume) of 50:50 or higher, such as 60:40 orhigher. In one embodiment, the sol is prepared using a drop ratio of99:1 or less. In one embodiment, the sol is prepared using a drop ratioof from 50:50 to 99:1.

In one embodiment, the drop ratio is controlled to be from about 60:40to 99:1.

By controlling the drop ratio to be at the lower end of the range, e.g.from 50:50 to 80:20, or from 50:50 to 78:22, or from 50:50 to 75:25, orfrom 60:40 to 75:25, or from 70:30 to 75:25, smaller micelles areobtained and thus a smaller pore size (diameter). In one embodiment, thedrop ratio is controlled to be from about 60:40 to 80:20.

By controlling the drop ratio to be at the higher end of the range, e.g.from 80:20 to 98:2, or from 82:18 to 98:2, or from 82:18 to 95:5, orfrom 85:15 to 98:2, or from 85:15 to 95:5, larger micelles are obtainedand thus a higher pore size (diameter). In one embodiment, the dropratio is controlled to be from about 80:20 to 95:5.

Controlled Flocculation by pH Control

When the titania sol is produced from a TiO₂ containing slurry the pH ofthe slurry can be controlled in order to the affect the extent to whichthe titania sol is flocculated.

In using this feature, the nano titania sol used in the process isflocculated, such that the sol as provided for drying is flocculated toa desired extent. As discussed below, the flocculation can be controlledso as to control the pore size and/or specific surface area and/orparticle shape of the resultant dried titania particles.

The pH may be adjusted to be closer to the iso-electric point of thetitania, so there is a greater degree of flocculation, or the pH may beadjusted to be further from the iso-electric point of the titania, sothere is a lesser degree of flocculation.

The iso-electric point is normally at a pH of from 5 to 6.

The pH adjustment may be effected using acid (to lower the pH) or usingbase (to raise the pH).

For example, a strong monoprotic acid may be used, e.g. a monoproticacid that has a pKa less than or equal to −1.0, especially one having apKa less than or equal to −1.5, and in one embodiment having a pKa lessthan or equal to −1.74. Examples of acids that may be used includehydrochloric acid, hydrobromic acid and nitric acid. Preferablyhydrochloric acid is used.

In another embodiment, a strong monoprotic base may be used, e.g. amonoprotic base that has a pKb less than or equal to 1.0, especially onehaving a pKb less than or equal to 0.5, and in one embodiment having apKa less than or equal to 0.3. Examples of bases that may be usedinclude sodium hydroxide and potassium hydroxide.

Therefore in the controlled flocculation of the present invention, acidor base may be added in a controlled manner such that the pH is adjustedto be close to the iso-electric point or away from the iso-electricpoint.

When the pH is adjusted to be close to the iso-electric point, theslurry is less dispersed (more flocculated). This leads towards largerpore sizes. It also leads towards particles that have a rough outersurface and that appear “fluffy”. Thus in one embodiment, if suchcharacteristics are desired, the pH can suitably be adjusted to be inthe range of from 4 to 7, preferably from 4.5 to 6.5, such as from 5 to6.

In one embodiment the pH is adjusted to be within 2.5 pH units of theiso-electric point, preferably within 2 pH units, more preferably within1.5 pH units, and most preferably within 1 pH unit of the iso-electricpoint, so as to obtain larger pore sizes and/or to obtain particles thathave a rough outer surface and that appear “fluffy”.

When the pH is adjusted to be away from the iso-electric point, theslurry is more dispersed (less flocculated). This leads towards smallerpore sizes. It also leads towards particles that have a smooth outersurface and that are either toroidal or spherical. Thus in oneembodiment if such characteristics are desired, the pH can be adjustedto be in the range of from 0.5 to 4, preferably from 1 to 3.5, or from 1to 3, such as from 1.5 to 3. Alternatively, the pH can be adjusted to bein the range of from 7 to 12, preferably from 7.5 to 11.5, such as from8 to 11.

In one embodiment the pH is adjusted to be 3 pH units or more from theiso-electric point, preferably 3.5 pH units or more from theiso-electric point, more preferably 4 pH units or more from theiso-electric point, and most preferably 4.5 pH units or more, such as 5units or more, or 5.5 units or more, from the iso-electric point, so asto obtain smaller pore sizes and/or to obtain particles that have asmooth outer surface and that are either toroidal or spherical.

During formation of a titania sol it is known to peptise the slurry.This is carried out using acid, especially a strong monoprotic acid,e.g. a monoprotic acid that has a pKa less than or equal to −1.0,especially one having a pKa less than or equal to −1.5, and in oneembodiment having a pKa less than or equal to −1.74.

Examples of acids that may be used for peptisation include hydrochloricacid, hydrobromic acid and nitric acid. Preferably hydrochloric acid isused.

Therefore in one embodiment of the controlled flocculation of thepresent invention, this peptisation step may be carried out in acontrolled manner such that the pH is adjusted either to be closer tothe iso-electric point or to be away from the iso-electric point.

Controlled Flocculation by Iso-Electric Point Control

When the titania sol is produced from a TiO₂ containing slurry theiso-electric point of the titania can be controlled in order to theaffect the extent to which the titania sol is flocculated.

In using this feature, the nano titania sol used in the process isflocculated, such that the sol as provided for drying is flocculated toa desired extent. The flocculation may occur during the formation of thesol or after its formation. However, the sol as provided for drying mustbe flocculated.

As discussed below, the flocculation can be controlled so as to controlthe pore size and/or specific surface area and/or particle shape of theresultant dried titania particles.

The iso-electric point may be adjusted so as to be closer to the pH ofthe slurry/sol, so there is a greater degree of flocculation, or theiso-electric point may be adjusted to be further from the pH of theslurry/sol, so there is a lesser degree of flocculation.

The iso-electric point is normally at a pH of from 5 to 6. However, thisiso-electric point can be adjusted, e.g. by the addition of adispersant, which can raise or lower the iso-electric point.

It may be that the iso-electric point is adjusted before, during orafter the peptisation stage of sol formation. In one embodiment, thisadjustment may be carried out at the peptisation stage of sol formation.

When the iso-electric point is adjusted to be close to the pH, theslurry is less dispersed (more flocculated). This leads towards largerpore sizes. It also leads towards particles that have a rough outersurface and that appear “fluffy”.

Therefore it may be that in one embodiment the iso-electric point isadjusted to be within 3 pH units of the pH, preferably within 2.5 pHunits, more preferably within 2 pH units, e.g. within 1.5 units, andmost preferably within 1 pH unit of the pH, so as to obtain larger poresizes and/or to obtain particles that have a rough outer surface andthat appear “fluffy”.

When the iso-electric point is adjusted to be away from the pH, theslurry is more dispersed (less flocculated). This leads towards smallerpore sizes. It also leads towards particles that have a smooth outersurface and that are either toroidal or spherical.

Therefore it may be that in one embodiment the iso-electric point isadjusted to be 3 pH units or more from the pH, preferably 3.5 pH unitsor more from the pH, more preferably 4 pH units or more from the pH, andmost preferably 4.5 pH units or more, such as 5 units or more, or 5.5units or more, from the pH, so as to obtain smaller pore sizes and/or toobtain particles that have a smooth outer surface and that are eithertoroidal or spherical.

In one embodiment, the controlled flocculation is achieved by contactingthe nano titania sol with a dispersant.

The dispersant may suitably comprise one or more dispersant materialselected from: water soluble carboxylic acids, water soluble salts ofcarboxylic acids, water soluble polycarboxylic acids, water solublesalts of polycarboxylic acids, phosphates and silicates.

In one embodiment, the water soluble carboxylic acid is an α-hydroxycarboxylic acid. The α-hydroxy carboxylic acid may comprise one, two orthree carboxylic acid groups. Examples of the α-hydroxy carboxylic acidthat can be used are lactic acid, glycolic acid, malic acid, tartaricacid, mandelic acid and citric acid.

In another embodiment, the water soluble carboxylic acid is a β-hydroxycarboxylic acid.

The water soluble polycarboxylic acid may be a dicarboxylic acid or atricarboxylic acid.

In general, citric acid may be a preferred choice due to its low costand ready availability.

The dispersant will be added to the sol at a level so as to achieve thedesired adjustment of the iso-electric point and hence to cause eithermore or less flocculation. Greater flocculation will lead to a largersize for the flocculated particles.

In one embodiment, the dispersant is added to the sol in an amount offrom 0.1 to 15 wt %, such as from 0.2 to 12 wt % or from 0.5 to 10 wt %.

In general, the slurry will be at a pH close to the natural iso-electricpoint and therefore the use of a low amount of dispersant ensures thatthere is closeness between the iso-electric point and the pH. This leadsto larger pore sizes and higher specific surface areas for the titaniaparticles. For example, the amount of dispersant may be from 0.1 to 5 wt%, such as from 0.3 to 4 wt % or from 0.5 to 3 wt %, e.g. from 1 to 2.5wt %.

In contrast, the use of a higher amount of dispersant ensures that thereis a greater gap between the iso-electric point and the pH. This leadsto smaller pore sizes and lower specific surface areas for the titaniaparticles. For example, the amount of dispersant may be from 6 to 15 wt%, such as from 7 to 13 wt % or from 8 to 12 wt %, e.g. about 9 to 10 wt%.

Controlled Drying During Preparation of Dried Titania Particles from aTitania Sol

In the process of the present invention, once a suitable flocculated solhas been provided, the sol is then subjected to a drying process.

The temperature used during the drying step can be controlled so as tocontrol the morphology of the resultant dried titania particles.Preferably, the temperature is controlled so as to control the particleshape of the resultant dried titania particles.

A higher drying temperature results in toroidal (doughnut shaped)particles and a lower drying temperature results in more sphericallyshaped particles.

In one embodiment, the drying temperature is from 50 to 350° C., such asfrom 75 to 325° C., or from 100 to 300° C.

The use of a lower drying temperature results in more spherically shapedparticles. For example, the drying temperature may be from 50 to 150°C., such as from 75 to 140° C., or from 100 to 125° C.

The use of a higher drying temperature results in more toroidal shapedparticles. For example, the drying temperature may be from 160 to 350°C., such as from 200 to 300° C., or from 220 to 280° C.

The drying process may suitably be spray drying or thermal drying.Preferably the drying process is spray drying.

The sol as dried may in one embodiment have a solids content of from 1%to 35% wt/wt, e.g. from 2 to 25% wt/wt or from 5 to 20% wt/wt or from 10to 18% wt/wt.

Of course, if when using the process of the invention it is decided tonot control the particle shape by use of the drying temperature, anyknown drying process may be used. This includes freeze drying, thermaldrying and spray drying.

Optional Steps

It may be that the titania particles are washed, but this is notessential. If the particles are washed, it may be that the washing iscarried out to reduce the level of salts and thus the conductivity. Inone embodiment washing is carried out to give a conductivity of lessthan 2 ms/cm.

As the salt level (and therefore conductivity) is reduced, shielding ofcharges decreases enabling repulsive forces to be expressed andconsequently free reconfiguration of particles and tighter packing isallowed. This means that a higher surface area can be achieved. Inaddition, the gelling behaviour of the sol appears to reduce when theconductivity is lowered, and higher concentrations of particles in thesol may be possible.

In another embodiment, however, the particles are not washed.

Optional Components

Depending on the intended end use of the titania, other components canalso be present during the manufacture of the titania. These may, forexample, be incorporated into the sol before the sol is dried.

In one embodiment, one or more active catalytic components, such astungsten or vanadium, are included during the manufacture of the titaniaparticles. These make the product suitable for catalytic reductionunits, such as SCR (selective catalytic reduction) units for automobileand static applications.

In another embodiment, one or more thermal stabiliser components, suchas silica, ceria or lanthana, are included during the manufacture of thetitania particles. These assist with ensuring large specific surfaceareas can be maintained when the product is used in applications whereelevated temperatures occur.

In another embodiment, one or more templating agents, such aspolystyrene latex nano spheres (PSL), may be used. PSL or any othertemplating agent can be mixed with the sol prior to dying. The resultantparticle can then be further heat treated to remove the templating agentto form highly porous particles. Templating agents are known to thoseskilled in the art and the use of templating agents is discussed in, forexample, Nandiyanto et el, Chemical Engineering Journal 152 (2009)293-296.

By the use of one or more templating agent, the products obtained by theinvention can be provided with a higher level of internal pores.

Uses

The present invention may be used to manufacture titania particlessuitable for use in numerous applications, as described further below.Dependent on the intended use, the skilled person will be able toidentify desired morphology characteristics of the titania, e.g. interms of pore size and/or particle shape, and can then control themanufacturing method as described above to obtain said desiredcharacteristics.

One preferred use of the particles is in the manufacture of catalystproducts, e.g. the particles may be used as a catalyst support, butother suitable end uses are also contemplated, as discussed below.

Emissions Catalysts

The titania particles may be produced in a manner that gives rise tolarge pore sizes, and hence high surface areas, when end uses areenvisaged that involve providing the titania as a catalytic support,such as in relation to emissions catalysts.

The titania particles may be used as a carrier for catalysts used toreduce or eliminate noxious gases prior to release to the atmosphere.Examples of uses include applications in mobile road systems (such ascars, motorcycles and trucks); mobile non-road applications (such asrail and marine) and static applications (such as power stations andwaste incinerators).

Catalysts that can be provided on the titania particles includeruthenium, rhodium, palladium, iridium, platinum, osmium, iron, cobalt,nickel, copper, silver, vanadium, tungsten, chromium and molybdenum. Inthese fields platinum, palladium and vanadium tend to be preferred.These catalysts can convert nitrogen oxides, carbon monoxide and sulphuroxides into less noxious substances. Tungsten is also used, especiallyin selective catalytic reduction.

Selective catalytic reduction (SCR) of nitrogen-based gases is possiblein the presence of ammonia. These nitrogen-based gases include nitricoxide (NO), nitrogen dioxide (NO₂) and nitrous oxide (N₂O); these havedetrimental affects environmentally such as contributing to ground levelozone, generation of acid rain and global warming. They also causeand/or aggravate medical issues, such as respiratory problems.

Removal of these gases can be achieved by passing emissions gasestogether with ammonia over a catalyst, such as platinum or vanadium.

In order to achieve high efficiencies, a large surface area is requiredpermit a maximum contact of the gas to the unit area of catalyst.Titania, alumina and zeolites are common catalytic carriers that canprovide this large surface area.

There are two main manufacturing processes: i) extruded ceramichoneycomb made from titania, alumina or zeolites, with the activecatalysts mixed into the carrier prior to extruding and ii) a ceramic ormetal honeycomb, which is then dipped into a slurry containing titaniaand the active catalysts, which is then dried; this is known as awashcoat.

In one embodiment, the catalytic porous titania is present on a support.Examples of support materials include glass, ceramic, metal, plastic,cement, concrete, asphalt, textile and paper. The support may be porousor non-porous. Examples of porous supports include a mat of fibers, azeolite, or a porous film. The term “on a support” refers to thecatalytic porous titania being provided on at least a portion of asurface of the support. If the support is porous, the term “on asupport” further includes the possibility that catalytic porous titaniais present within some or all of the pores of the support.

In one embodiment, the titania particles can be used as a carrier orwashcoat for selective catalytic reduction units. In such an embodiment,it will be desired to prepare titania particles that have large poresizes, because then the porous titania will impart a large surface area.

In one such embodiment, the titania particles may be prepared so as tohave a toroidal shape because this shape may lend itself to improvedpermeability when used in applications such as selective catalyticreduction (SCR) units for automobile and static applications.

In another embodiment, when preparing the particles, the titania sol maybe mixed with active catalysts prior to spray drying. In such anembodiment, it will be desired to prepare titania particles that havelarge pore sizes, because then the porous titania will impart a largesurface area. This will result in a large surface area porous materialthat has catalytic activity. Such active catalysts include ruthenium,rhodium, palladium, iridium, platinum, osmium, iron, cobalt, nickel,copper, silver, tungsten, vanadium, chromium and molybdenum.

In yet another embodiment, titania particles are prepared that havelarge pore sizes, because then the porous titania will impart a largesurface area, and the titania sol is mixed with compounds prior to spraydrying that help maintain its large surface area when exposed toelevated temperatures. In this regard, it is known that titania used forceramic extrusions or as washcoats can be prone to a reduction insurface area as a result of the elevated temperatures at which thecatalysts are operated. By using certain compounds, this effect can bemitigated. These compounds include tungsten (vi) oxide from a precursorsuch as ammonium metatungstate or ammonium paratungstate, lanthanumoxide from a precursor such as lanthanum nitrate hexahydrate, ceriumoxide from a precursor such as cerium nitrate hexahydrate and silicafrom a precursor such as silicic acid. One or more such compounds may beused. Such compounds may be added to the sol prior to spray drying.These may be incorporated immediately prior to spray drying, or may beadded during parts of the sulphate process. For example, ammoniummetatungstate may be incorporated into the precipitation step of thesulphate process.

Another embodiment is the use of porous titania in the manufacture ofdiesel particle filter (DPF)/SCR combination units. In an effort toreduce unit size, while maintaining efficacy, manufacturers areattempting to combine these two units within emission control systems.However, by using conventional titania as the filter, increased backpressure will ensue due to the poor porosity of the structure. The useof porous titania will permit a gas flow through the filter with reducedback pressure but maintain a good gas to solid contact ratio.

In one embodiment of the invention the titania particles may be preparedso as to have a toroidal shape because this shape offers improvedpermeability for gas flow (DPF) as well as improved specific surfacearea for the selective catalytic reduction (SCR).

In addition, the titania may be coated with silica or the like toprovide improved thermal stability.

Chemical Catalysis

The titania particles may be produced in a manner that gives rise tolarge pore sizes, and hence high surface areas. This may be beneficialwhen end uses are envisaged that involve providing the titania as acatalytic support, such as in relation to chemical catalysts.

Examples include the desulphurisation of gases in the petroleum industryby the Claus process, whereby the porous titania beads act as a catalystto promote the hydrolysis of carbonyl sulphide and carbon disulphide tohydrogen sulphide and carbon dioxide. Titania is known to give animproved conversion rate compared to alumina based catalysts. In oneembodiment, the porous titania will impart improved gas to solid contactand so enhance chemical catalysis processes such as the Claus process.

In another embodiment, the porous titania may be mixed with a binder andextruded to create high surface area titania pellets for use as achemical catalyst or chemical catalyst support.

In yet another embodiment, the porous titania beads or extrudate mayundergo an impregnation process, whereby catalytic promoters such asmolybdenum, nickel, cobalt etc. or a mixture thereof, may be impregnatedinto the pores of the porous titania.

In another embodiment, the addition of a thermal stabiliser (such asammonium metatungstate or ammonium paratungstate, lanthanum oxide from aprecursor such as lanthanum nitrate hexahydrate, cerium oxide from aprecursor such as cerium nitrate hexahydrate and silica from a precursorsuch as silicic acid) may be used to improve catalyst performance bymaintaining a high BET surface area at elevated temperatures.

Photocatalytic Embodiments—Self Cleaning, Antibacterial, AirPurification

The titania particles may be produced in a manner that gives rise tolarge pore sizes, and hence high surface areas. This may be beneficialwhen catalytic end uses are envisaged, such as in relation tophotocatalysis.

It is well known that TiO₂ is an efficient and benign photocatalyst.Photons with an energy greater than or equal to the band gap of TiO₂(3.2 eV for the anatase phase) that strike a TiO₂ crystal, energise anelectron which in turn jump from the valance band into an unoccupiedconduction band. This results in electron pairs in the conduction bandand positive electron holes in the valence band. These in turn can thenreact with O₂ to form the hydroxyl radical of O₂ ⁻ and with H₂O to formthe hydroxyl radical OH respectively. These radicals are extremelyreactive and will degrade organic matter.

In one embodiment, a porous titania with a large surface area can beprovided, as this will result in more electron pairs and holes at thesurface and will therefore be more photocatalytic. It may be used forself cleaning purposes when incorporated into materials such as exteriorcoatings, concrete, tiles, extruded ceramic fascias, plastics, textilesetc.

In another embodiment, a titania material that is porous but that is notnano sized (e.g. with a particle size of 1 micron or more) can beprovided, which will result in lower degree of light scattering/lowerrefractive index, permitting the porous titania to be used for selfcleaning in coloured systems while having a lower tinting strengthcompared to pigmentary titania.

In another embodiment, dopants can be added during the production of thetitania particles. This leads to further improvements in catalyticefficacy in the porous titania. Additionally, certain dopants can alterthe band gap and so can alter the responsiveness of the catalyst atdifferent wavelengths of light. Examples of dopants include i) noblemetals: gold, nickel, nitrogen, palladium, platinum, rhodium, silver,tin and vanadium, ii) cationic metals: aluminium, cerium, chromium,cobalt, copper, erbium, europium, gadolimium, iron, lanthanum,manganese, molybdenum, neodymium, nickel, osmium, praseodymium, rhenium,ruthenium, samarium, vanadium and zinc and iii) anionic non-metals:carbon, fluorine, nitrogen, phosphorus and sulphur.

In one embodiment, the catalytic porous titania may be mixed with areactant fluid and irradiated with visible light to provide for achemical reaction of one or more components of the reactant fluid. Thecatalytic porous titania may then be recovered from the fluid andrecycled for use in another portion of the reactant fluid. The catalyticporous titania may be used in place of general metal catalysts such ascobalt, nickel, copper, gold, iridium, lanthanum, nickel, osmium,platinum, palladium, rhodium, ruthenium, silver, strontium, yttrium,zirconium and tin.

In another embodiment, the catalytic porous titania is present on asupport, and the reactant fluid may flow in contact with the support andthe composition, and when irradiated with light, provides for a chemicalreaction of one or more components of the reactant fluid. In thisconfiguration, the catalytic porous titania may be exposed to a constantstream of fluid and does not require separation of the catalytic poroustitania from the fluid after the reaction is performed. For example, acatalytic porous titania may be applied to a support, for example anautomobile exhaust system, where the exhaust system has been fitted witha visible or UV light source, such as a fiber optic light source or anLED light source. Irradiation of the catalytic porous titania duringoperation of the automobile engine may provide for degradation oforganics and other pollutants generated in the engine intoenvironmentally acceptable substances.

In another embodiment, the catalytic porous titania may be present on asurface that is contacted with various environmental contaminants orpollutants, such as dirt, grease and other organic and inorganiccontaminants and pollutants. The catalytic porous titania, optionally inthe form of a formulation comprising the catalytic porous titania, isapplied to the surface and the surface is irradiated with UV/visiblelight while the contaminants or pollutants contact the surface. Uponexposure to UV/visible light, the surface becomes “self-cleaning”because it degrades or inactivates the contaminants or pollutants. Forexample, self-cleaning glass may have a transparent or translucentcoating of the catalytic porous titania applied on one or both sides ofthe glass. Contaminants that contact the glass may then be degraded whenthe glass is exposed to UV/visible light.

In another embodiment, the catalytic porous titania may be present on asurface that is exposed to microbes (such as bacteria and fungi) and/orviruses. Upon exposure to UV/visible light, such a surface may be a“disinfecting surface” because it destroys or inactivates microbesand/or viruses that are present on the surface. For example, surfaces inresidential, commercial or hospital environments may have a coating ofthe catalytic porous titania applied on the surface. Microbes and/orviruses that contact the surface may then be destroyed or inactivatedwhen the surface is exposed to UV/visible light. Examples of surfacesthat may be made into disinfecting surfaces include countertops,flooring, walls, handles, switches, knobs, keypads, telephones, bedframes and surfaces of medical instruments.

The catalytic porous titania may also be applied to a surface to providetemporary disinfection of the surface. For example, the catalytic poroustitania may be introduced into a cleaning composition. The cleaningcomposition may be in the form of a liquid, foam or a lotion.Application of the cleaning composition to a surface, followed byexposure of the surface to UV/visible light, may cause the destructionor inactivation of microbes or viruses that are present on the surface.Such cleaning compositions may be formulated for use on skin to providea disinfecting personal care product.

In yet another embodiment, the catalytic porous titania may be used incomposite materials, including polymer composites, fabrics and nonwovenmaterials. For example, the catalytic porous titania may be incorporatedwith fibers into textile fabrics. These fabrics may provide fordegradation of contaminants in contact with the fabric when exposed toUV/visible light, resulting in self-cleaning and/or self-disinfectingfabrics.

The catalytic porous titania may also be used for air and/or waterpurification. For example, the catalytic porous titania may be mixedwith contaminated air or water and irradiated with UV/visible light.Contaminants in the air or water may be degraded into substances thatare volatile or that are more easily separated from the air or water.For example, contaminants containing organic substances and halogenatedsubstances may be degraded into carbon dioxide and halide ions, whichmay then be separated from the air or water. In the case of airpurification, the degradation of contaminants such as NO and NO₂ eitherindividually or collectively and VOCs may also result in cleaner air andcontrol of odours in the air.

Drug Release

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be hollow, or porous with large size pores, orspherical with highly rough surfaces. These titania particles may beused as a carrier in a drug delivery system, whereby the activeingredient is impregnated into the hollow particle or into the pores ofthe highly porous particle.

The low density, porous particles are ideal for pulmonary drug deliverydue to their aerodynamic shape which gives rise to good pulmonarydispersibility.

In another embodiment, titania particles may be prepared in accordancewith the invention so as to be hollow, or porous with large size pores,or spherical with highly rough surfaces, and these particles areimpregnated with an active ingredient and then coated in a degradablecoating, whereby the coating is degraded following delivery, e.g. to theGI tract. Types of delivery include immediate, thermo-sensitive releaseand controlled release.

Another embodiment involves the preparation of titania particles withlarge pore sizes in a method whereby there is also impregnation ofmagnetite, or another detectable substance, into the porous titania.Alternatively, the titania particles with large pore sizes are prepared,followed by the encapsulation of magnetite (or another detectablesubstance) by spray drying the titania sol with the magnetite or otherdetectable substance. The particles prepared in this manner are suitablefor use as intravascular probes for diagnostic purposes such as imaging.

Another embodiment involves the preparation of titania particles withlarge pore sizes and/or hollow titania particles and/or highly roughspherical titania particles, in a method whereby there is alsoimpregnation of active substance(s) into the hollow/porous/roughsurfaced titania. These particles may be used as a drug delivery systemused for both active and passive targeting.

Biodegradable Packaging

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be hollow, or porous with large size pores, orspherical with highly rough surfaces. These titania particles may beused as a means to biodegrade packaging following a predetermined timeperiod.

This involves encapsulating the particle with a compound that willphoto-catalytically degrade over a predetermined time period. Saidparticle will then over time start to photo-catalytically degrade thepackaging into which it is incorporated.

Nb Dope for Conductive Coatings

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be hollow, or porous with large size pores. Thesetitania particles may be doped with niobium. Accordingly, thesemiconductor nature of the titania can be modified, so that theparticles instead become a conductor. The particles may then be used inconductive coatings.

In this respect, it is possible to create conductive coatings based onsuch doped particles for use in display screens or organic lightemitting diodes. Porous or hollow titania particles that have arelatively large particle size (above nano size, e.g. 1 micron indiameter or more) exhibit a lower degree of light scattering compared totitania manufactured for its pigmentary properties. As a result, it ispossible to create a transparent coating which can be utilised fordisplay purposes.

In one embodiment, porous or hollow titania particles are produced bythe process of the invention and that have been doped with niobiumduring the production process. These exhibit transparency andconductivity and can be used in applications such as display screenequipment or organic light emitting diodes.

Dye Sensitised Solar Cells (DSSCs)

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be porous with large size pores and so as to havea high surface area.

The semiconductor properties of the titania, in combination with thislarge surface area and highly porous structure, means these particlesmay be used as semiconductor films in DSSCs (Dye Sensitised SolarCells).

For example, an electric current is produced when dye molecules areexcited by exposure to light. The excited dye molecules transferelectrons into the conduction band of the titania material, whichconducts the electrons to a current collector connected to an electricalcircuit with a load. The highly porous structure of the titania gives ahigh surface area and therefore a high level of absorption of dyemolecules onto the porous titania structure thus resulting in increasedcell efficiency.

In a further embodiment, the porous titania material may be used as asemiconductor film in a flexible DSSC. Low temperature curing ispossible due to the improved primary particle contacts in the aggregatedparticles, thus resulting in effective electrical conductivity acrossthe particles. For example, a DSSC can be created on a flexible plasticsubstrate that requires low curing temperatures.

In yet another embodiment, a sensitizing dye for use in DSSCs can beadded into the pore structure of the titania during manufacture of thetitania or after the dried titania has been obtained. The material wouldtherefore be supplied pre-loaded with dye, thus eliminating the lengthyprocess of dying the electrode when fabricating DSSCs. This would reduceboth the time and complexity of DSSC production, and potentiallyincrease the dye absorption onto the catalytic material, thereforeincreasing the potential efficiency of the cell.

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be porous with a controlled size of pores.

In DSSC applications it can be useful for the titania particles can havetheir pore structures specifically “tuned” for the end use. In the DSSCapplications, the TiO₂ has dye adsorbed onto its surface and the moredye that is accessible by the electrolyte, and the more that is incontact with the TiO₂, the better the electron transfer. Therefore bytuning the pore system (e.g. in terms of the number of pores, size ofpores), the potential efficiency of the solar cell can be improved.

UV Protection

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be porous with large size pores and so as to havea high surface area. Preferably the particles are larger than nano size,e.g. 1 micron in diameter or more.

Due to these particles having a relatively large particle size, alongwith the highly structured porous nature, similar to that of an aerogel,the particles will have a low refractive index. Therefore the particlescan be used to provide a material, e.g. a coating, with UV protectionproperties. The material may be transparent.

In one such embodiment the porous titania can be given a coating ofsilica; this would lock in the photo-activity of the TiO₂, and hencemake an excellent product for UV protection.

These particles could be used in personal care products and cosmeticformulations, such as sunscreens, moisturizers, color foundations,lipstick, lip balm, foot care products and ointments. These particlescould also be used in coatings and masonry formulations, such as inautomotive coatings, wood coatings, building coatings, glass coatings,flooring, swimming pool surfaces, and cement or concrete coatings.

In one embodiment the porous titania particles could be silica coated toprovide an effective UV protector for use in plastics. For example, thesilica coated particles could be incorporated into a polymer, such asplastic containers, window frames, building sidings or the like, andcould provide protection to the polymer from UV light. This would leadto greater durability and life span of the plastics exposed to UV light.

In another embodiment the particles may be encapsulated in silica, forexample a stable nano silica sol may be mixed with the TiO₂ sol prior todrying. The mix would then be spray dried in conditions to favorencapsulation; this would result in a titania bead encapsulated insilica, due to the smaller silica nano particles migrating to the outeredge of the droplet in the spray drying process. This would provide aparticle fully encapsulated in silica and therefore provide a particlewith effective UV protection properties that could be used in anysituation where a UV protective coating is required.

In further embodiments the porous titania material can be doped withmetals, such as Fe, Cr, Mn, Ce, Ni, Cu, Sn, Al, Pb, Ag, Zr, Zn, Co, Moand W, or non-metals such as B, C, N, P, As, S, Se, Te, F, Cl, Br and I.Doping with these elements can cause a increase in the catalyticproperties and/or a decrease in the catalytic properties; therefore itis possible to increase the UV protection properties. For example, aco-precipitation can be used to dope transition metals into the titaniumdioxide lattice, whereby a dopant is added to the titania sulphateliquor; this is then precipitated out resulting in doped titania. Thiswould then improve the UV protection due to a change in band gap toreduce the photo-catalysis.

In a further embodiment the porous titania may be subject tocalcination; this converts the crystal structure from the anatasestructure to the rutile structure. This therefore makes the particlesless photoactive, as the rutile structure of titanium dioxide is lessphotoactive than that of the anatase form. Of course, rutile titaniaparticles may also be prepared in the sol in the first place. Use ofrutile titania may be helpful in UV protection applications such asthose noted above.

CICPs (Complex Inorganic Coloured Pigments)

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be porous with large size pores and so as to havea high surface area.

This porous titania material can be used as a base for CICP materials,due to its highly porous nature and high surface area.

For example, the titanium dioxide base can be combined with one or moremetal ions, such as antimony, chromium, nickel, manganese, iron,niobium, tin, tungsten, vanadium, zinc or cobalt. The mix can then becalcined to give highly coloured, high chroma pigments.

Water Splitting

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be porous with large size pores

In one such embodiment, the porous titania material may be used as acatalytic material for the production of hydrogen and oxygen via watersplitting.

For example, water containing the catalytic composition may bedecomposed into hydrogen and oxygen by photo-catalysis when the water isirradiated with UV/visible light. Alternatively this decomposition maybe carried out in a photo-chemical cell having a photo-anode containinga quaternary oxide. The use of a photo-electrochemical cell has thebenefit that it can provide for separate collection of hydrogen andoxygen from the cell.

Lithium-Ion Battery

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be porous with large size pores

In one such embodiment, the porous titania material may be used as anelectrode in a lithium-ion battery, due to the highly porous nature andthe good inter-particle contacts in the aggregated particle. Thisprovides efficient transport of lithium ions and favoured ion-exchangeratio, which results in a high value of charge/discharge capacity andgood kinetic characteristics. There are also fewer safety concerns thanwith use of conventional carbon negative electrode batteries.

Sensors

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be porous with large size pores and so as to havea high surface area.

In such an embodiment, the semiconductor and catalytic properties of thetitania can be used for sensing gases. Therefore the titania particlesmay be used as a sensor material.

The sensing process is mainly a surface process between the TiO₂ surfaceand the gas molecules; therefore the porous particles prove excellentcandidates, due to the highly porous structure and large surface area.

Titanium dioxide can be used as a gas sensor because the electricalconductivity of titanium dioxide can change depending on the chemicalcomposition of the environment. The electrical resistance of the titaniaparticles (or a material containing the titania particles) may bemeasured in an environment and compared with the electrical resistancein a control environment. The difference between the measured resistanceand the control resistance may be correlated with the amount and/oridentity of a gas in the environment.

Examples of gases that may be identified and/or measured includehydrogen, carbon monoxide, hydrogen sulfide, and water, acetone, ethanoland methanol. Certain titanium dioxide based gas sensors can be used atlow temperatures, whilst other are suited to elevated temperatures.

In a further embodiment the porous titania can be doped with metals suchas Al, Pd, Pt, Nb, Cr, Pt, Ta, K and La; this will improve theselectivity and sensitivity of the porous titania particles for use as agas analyser.

Fuel Cells

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be porous with large size pores and so as to havea high surface area.

In one such embodiment, due to the high surface area and itssemiconductor properties, the porous titania particles can be used as acatalyst support in a fuel cell, especially in proton exchange membranefuel cells (PEMFC).

A PEMFC works by using a fuel (usually hydrogen, but in some casesorganic compounds such as methanol). The fuel cell consists of an anode,cathode and an electrolyte. The anode consists of a catalyst (usuallyplatinum); this oxidizes the fuel. The positively charged particlestravel through a polymer electrolyte membrane whereas the negativelycharged electrons must run through an external circuit to the cathode,thus resulting in the generation of electricity. The cathode alsoconsists of a catalyst (usually platinum) to reduce the positivelycharged particles to H₂O.

The platinum catalysts are usually supported on a porous carbon support;however porous titania particles made by the process of the inventionwould prove a effective support medium, due to their large surface areaand excellent electron transfer properties. They will also have improvedstability as compared to carbon supports.

Water Purification

In one embodiment, titania particles may be prepared in accordance withthe invention so as to be porous with large size pores and so as to havea high surface area. Preferably the particles are larger than nano size,e.g. 1 micron in diameter or more.

In one such embodiment, the highly porous product with a large surfacearea and large particle size, in combination with its catalyticcomposition, means the porous titania particles can be used in the fieldof water purification. Therefore the titania particles may be used as awater purification material.

For example, the titania particles may be mixed with contaminated waterand irradiated with UV/visible light. Contaminants in the water may bedegraded into substances that are volatile or that are more easilyseparated from the water. For example, contaminants containing organicsubstances and halogenated substances may be degraded into carbondioxide and halide ions, which may then be separated from the water.

Currently problems arise with using nano titanium dioxide particles; theproblem lies with separating the nano particles from the water. Howeverthe porous titania particles made according to the process of theinvention can have a larger than nano particle size, thus filtering theTiO₂ particles from the water will be easier and more effective.

The particles still exhibit the beneficial properties of the nanotitania, however, such as large surface area and high photocatalyticactivity. Therefore the particles are as effective, if not moreeffective, than nano titanium dioxide particles.

In one such embodiment the porous titania particles can be doped withmetals, such as Fe, Cr, Mn, Ce, Ni, Cu, Sn, Al, Pb, Ag, Zr, Zn, Co, Moand W, or non-metals such as B, C, N, P, As, S, Se, Te, F, Cl, Br and I.This doping causes a change in the band gap and thus an increase in thephotocatalytic properties, therefore increasing the effectiveness of itsuse in water purification systems.

The invention will now be further described, in a non-limiting fashion,with reference to the following examples and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an image obtained by scanning electron microscopy (SEM) of theparticles of the product obtained in Example 2.

FIG. 2a is an image obtained using transmission electron microscopy(TEM) of the particles of the product obtained using 6% nucleation atprecipitation in Example 3.

FIGS. 2b-2f are images obtained using transmission electron microscopy(TEM) of the micelles produced by sulphate precipitation at nucleationlevels of 6%, 2%, 1%, 0.5% and 0.1%, respectively, in Example 3.

FIGS. 3a-3e are images obtained by scanning electron microscopy (SEM) ofthe particles of the products obtained in Example 4 at pH values of 5.5,4.5, 3.25, 2, and 1.5, respectively.

FIG. 4a is an image obtained by scanning electron microscopy (SEM) ofthe particles of the product obtained in Example 6 prepared using 15%silica as a dopant.

FIG. 4b is an image obtained by scanning electron microscopy (SEM) ofthe particles of the product obtained in Example 6 prepared using 10%WO₃ as a dopant.

FIGS. 5a-5d are images obtained by scanning electron microscopy (SEM) ofthe particles of the dried products obtained in Example 7 for a solhaving 1% solids at dryer inlet temperatures of 110° C., 150° C., 200°C., 250° C., respectively.

FIGS. 6a-6d are images obtained by scanning electron microscopy (SEM) ofthe particles of the dried products obtained in Example 7 for a solhaving 10% solids at dryer inlet temperatures of 110° C., 150° C., 200°C., 250° C., respectively.

FIGS. 7a-7d are images obtained by scanning electron microscopy (SEM) ofthe particles of the dried products obtained in Example 7 for a solhaving 17% solids at dryer inlet temperatures of 110° C., 150° C., 200°C., 250° C., respectively.

EXAMPLES Example 1

A concentrated anatase titania sol was obtained by a 6% nucleatedprecipitation that was carried out in accordance with the method ofWO2011/033286. Samples of the sol were thermally dried at (a) 105° C.and (b) 200° C.

The specific surface areas of each of the dried samples were testedusing the BET method.

Thermally Dried Sample Sample 105° C. 200° C. BET specific surface area280.9 311.2 (m²/g)

When repeated with a higher drying temperature being applied, theparticles were more toroidal in shape and had a higher specific surfacearea.

Example 2

A concentrated titania sol was prepared using clean Scarlino rutilenuclei (washed free of salts, 0.5 ms/cm). The sol was produced as inmethod outlined in WO2011/033286. In this regard, the washed Scarlinonuclei were peptised to pH 1.5, 10% citric acid was added, MIPA wasadded to take the pH to 8, and then the particles were washed to <2ms/cm.

The concentrated sol was then spray dried at 17% at 110° C. using a LabPlant Super 7 laboratory spray drier.

The specific surface area of the sample was tested using the BET method.The pore size and pore volume were measured by both mercury porosimetryand nitrogen isotherms.

BET SSA (m²/g) 87.52 Mercury Large Pore Size (μm) 1.7018 Mercury SmallPore Size (nm) 23.1 Nitrogen Large Pore Size (nm) 40.65 Nitrogen SmallPore Size (nm) 1.4 Pore Volume mercury (cm³/g) 0.36 Pore Volume nitrogen(cm³/g) 0.31

Scanning electron microscopy (SEM) was carried out to image theparticles of the product obtained. The obtained image is shown in FIG.1.

When the experiment is repeated with a higher drying temperature beingapplied, the particles become more toroidal in shape and have a higherspecific surface area.

Thus the invention applies for rutile material as well as anatase.

Example 3

Several different concentrated titania sol products were obtained byprecipitation that was carried out in accordance with the method ofWO2011/033286. These were obtained using different levels of nucleationat precipitation. One had a 1% nucleated precipitation, one had a 2%nucleated precipitation and one had a 6% nucleated precipitation.

Samples from each product were spray dried using a LabPlant SD-05laboratory spray drier.

The specific surface areas of each of the dried samples were testedusing the BET method.

The pore size was measured using mercury porosimetry, using aMicromeritics AutoPore IV porosimeter.

% Nucleation at precipitation 1 2 6 BET SSA (m²/g) 219.8 269.1 314.5Pore Size (nm) 9.5 6.7 4.3

It can be seen that by using a lower level of nucleation, the pore size(diameter) was higher.

This confirms what the present inventors have determined, namely that bycontrolling the extent of nucleation, and therefore by controlling themicelle size, the pore size in the resultant titania particles can becontrolled, with lower nucleation levels giving rise to larger poresizes in the resultant titania particles.

Accordingly, a desired set of properties in the end product can beobtained by suitable control of the parameters in the process ofmanufacture of the titania.

Transmission electron microscopy (TEM) was also carried out to image theparticles of the product obtained using 6% nucleation at precipitation.The obtained image is shown in FIG. 2 a.

Transmission electron microscopy (TEM) was then carried out to image themicelles produced by sulphate precipitation at nucleation levels of 6%,2%, 1%, 0.5% and 0.1%. The obtained images are shown in FIGS. 2b-2frespectively.

It can be seen that micelle sizes as large as 150 nm or more can beobtained with a nucleation level of 0.1% or lower. By increasing thenucleation level the size of the micelles decreases. Therefore controlof the micelle size can be exerted. As a consequence, the pore size inthe resultant titania particles can be controlled.

As discussed above, the present inventors have determined that bycontrolling the micelle size the pore size in the resultant titaniaparticles can be controlled, with larger micelles giving rise to largerpore sizes in the resultant titania particles.

Accordingly, a desired set of properties in the end product can beobtained by suitable control of the parameters in the process ofmanufacture of the titania.

Example 4

A range of concentrated slurries were obtained by Mecklenbergprecipitation, in accordance with the method of WO2011/033286. A 6%nucleation level was used at precipitation. The titania slurries werepeptised with a peptising agent to achieve various pH levels (1.5, 2,3.25, 4.5 and 5.5). Hydrochloric acid was used as the peptising agent.

The flocculation size of the slurries was determined using X-raysedimentation method on a Brookhaven machine (BI-XDC X-ray DiscCentrifuge).

pH from peptisation 5.5 4.5 3.25 2 1.5 Size of Flocculated 1319 962 95733 14 product in slurry (nm)It can be seen that at a pH close to the iso-electric point (pH 5-6)there is more flocculation and the slurry is less dispersed.

This leads towards larger pore sizes. It also leads towards particlesthat have a rough outer surface and that appear “fluffy”. This wasillustrated by the use of scanning electron microscopy.

In this regard, scanning electron microscopy (SEM) was carried out toimage the particles of the product obtained. The obtained images areshown in FIGS. 3a-e . FIG. 3a is pH 5.5, FIG. 3b is pH 4.5, FIG. 3c ispH 3.25, FIG. 3d is pH 2, and FIG. 3e is pH 1.5.

It can be seen that at a pH closer to the iso-electric point (pH 5-6),larger pore sizes are obtained and the particles have a rough outersurface and appear “fluffy”. As the pH moves further away from theiso-electric point, smaller pore sizes are obtained and the particleshave a smoother outer surface and are either toroidal or spherical.

Example 5

A range of concentrated sols were prepared by Mecklenberg precipitation,in accordance with the method of WO2011/033286. A 1.8% nucleation levelwas used at precipitation, peptisation was effected to pH 1.5, andcitric acid (dispersant) was added.

The sols were prepared with various levels of citric acid (1%, 2.3%, 3%and 10%) as the dispersant, to give a range of sols with differingextents of flocculation. Subsequently, MIPA was added to take the pH to8. The particles were then either left unwashed or were washed (to givea conductivity of <2 ms/cm). The sols were then spray dried using aLabPlant Super 7 laboratory spray dryer.

The dried samples were then analysed for surface area via the BET methodand porosity by both mercury porosimetry and nitrogen isotherms.

Citric Acid Level (%) 1 2.3 3 10 Conductivity(ms/cm⁻¹) 20.6 21.1 19.820.6 BET SSA (m²/g) 177.8 179.9 136 75.4 Mercury Large Pore Size 2.5991.9317 2.2885 1.5703 (μm) Mercury Small Pore Size 14.2 14.2 13.1 11.2(nm) Nitrogen Large Pore Size 39.6 42.5 33.5 26.5 (nm) Nitrogen SmallPore Size 0.67 0.67 0.66 0.64 (nm) Conductivity (ms/cm⁻¹) <2 <2 <2 <2BET SSA (m²/g) 248.8 254.1 258 239.6 Mercury Large Pore Size 1.81421.6069 1.59 1.9178 (μm) Mercury Small Pore Size 14.9 13.2 11.4 8.9 (nm)Nitrogen Large Pore Size 33.5 26.7 21.1 14.8 (nm) Nitrogen Small PoreSize 0.81 0.54 0.54 0.56 (nm)

When lower amounts of dispersant were used, the iso-electric point wascloser to the pH of the slurry. This resulted in the slurry being lessdispersed.

It can be seen from the results that this use of lower amounts ofdispersant (1% and 2.3%) leads to large surface areas, both in thewashed and unwashed products. The use of lower amounts of dispersant (1%and 2.3%) also leads to larger pore sizes in the particles, both in thewashed and unwashed products.

The porosity results show three distinct pore size regions:

-   -   >1 um=cavities between particles    -   5-20 nm=the pores within the particles (between the micelles)    -   ˜0.6 nm=pores within micelles.

The washing of the particles reduces the level of salt and therefore theconductivity. As the salt level (and therefore conductivity) is reduced,there are fewer charges present causing repulsion between particles andtherefore the particles can pack together more closely. In addition,gaps are left behind that were previously filled by salts. This meansthat a higher surface area can be achieved.

In addition, the gelling behaviour of the sol appears to reduce when theconductivity is lowered, and higher concentrations of particles in thesol may be possible.

Example 6

A range of sols were prepared using a Blumenfeld process with a 70:30drop ratio and a 10 minute drop time to give a modal micelle size of 23nm. One sol was prepared in the standard method outlined inWO2011/033286. Another sol was doped with 10% WO₃ in the form ofammonium metatungstate at precipitation, and then processed according tothe method outlined in WO2011/033286. A final sol was prepared with 10%silica added in the form of silicic acid; this was added after thepeptisation stage, by passing sodium silicate through an ion exchangecolumn to produce silicic acid, after this the sol was prepared as inWO2011/033286.

The sols were then spray dried using a Lab Plant Super 7 laboratoryspray dryer.

Scanning electron microscopy (SEM) was carried out to image theparticles of the doped products obtained. The obtained images are shownin FIGS. 4a-b . FIG. 4a is 15% silica, FIG. 4b is 10% WO₃.

The spray dried porous titania samples were then calcined at 500° C. for5 hours, 1 day, 3 days and 7 days. The specific surface areas of thecalcined samples were then measured via the BET method.

BET SSA after calcination at 500° C. (m²/g) Variant Control 5 hrs 1 day3 days 7 days Standard 301.3 84.8 77.7 70.5 65.3 Std + 10% 257.7 113.6112.5 102.0 100.4 WO₃ Std + 15% 278.1 265.2 262.8 257.2 255.4 SiO₂

It can be seen that the use of dopants gives rise to improved thermalstability. In particular, the use of the SiO₂ dopant leads to a productwhere the particles are sufficiently stable to retain their largesurface areas even after high temperature calcination for prolongedperiods of time.

Example 7

A range of sols were prepared by the Mecklenberg method with a 6%nucleation level at precipitation. The sols were prepared in thestandard way and the diluted to different levels to give sols at a rangeof solids content (1%, 10%, 17% & 25% wt/wt % solids).

The sols were then dried via a Lab Plant laboratory spray dryer, andparticle size measured via the laser diffraction method using a MalvernInstruments Ltd MasterSizer instrument.

Dryer Feed Concentration (wt/wt %) 1% 10% 17% 25% Particle Size 3.056.75 8.59 10.17 (μm) Malvern

Therefore it can be seen that particle size can be controlled bycontrolling the solids content of the spray dryer feed, with highersolids contents leading to larger particles.

The inlet temperature to the dryer was altered (110° C., 150° C., 200°C., 250° C.) to assess the effect of this drying temperature on solswith 1% solids, 10% solids and 17% solids.

Scanning electron microscopy (SEM) was carried out to image theparticles of the dried products obtained. The obtained images are shownin FIGS. 5a-d (1% solids), FIGS. 6a-d (10% solids) and FIGS. 7a-d (17%solids).

In each case, image a is after drying at 110° C., image b is afterdrying at 150° C., image c is after drying at 200° C. and image d isafter drying at 250° C.

Therefore it can be seen that particle shape can be controlled via thespray dryer inlet temperature. A lower inlet temperature gives morespherical particles (which can be hollow), whilst a higher temperatureleads to the formation of toroidal (doughnut shaped) particles.

Example 8

A concentrated titania sol was obtained by precipitation that wascarried out in accordance with the method of WO2011/033286.

The samples used were from a 6% nucleated Mecklenburg precipitation,that had been peptised to pH 1.5, addition with 10% citric acid, MIPAneutralised and CFF washed to <2 ms/cm.

The sol was spray dried using a laboratory scale Lab Plant Super 7 spraydryer, to form porous spherical particles. The sol was at a solidsconcentration of 17% wt/wt, and was spray dried at a temperature of 110°C.

The dried particles were then dispersed in water at a concentration of100 g/l.

The resulting dispersion was then milled for 30 minutes using a highshear Silverson mixer. The particle size was measured using a MalvernInstruments Ltd MasterSizer laser diffraction instrument. Measurementswere taken prior to milling (0 minutes), during milling (at 10 minutesand 20 minutes) and after milling (at 30 minutes).

Milling time 0 min 10 min 20 min 30 min d(v, 0.1) μm 2.24 1.99 1.95 1.98d(v, 0.5) μm 6.55 6.09 5.98 5.79 d(4, 3) μm 8.05 6.89 6.55 6.18 d(v,0.9) μm 14.64 12.64 11.9 10.81 Modal particle size μm 7.99 7.15 7.137.02

This shows that the particles obtained are very stable under high shearforces.

The experiment was then repeated but with the spray dried particlesbeing thermally treated at 500° C. for 7 days prior to milling, in orderto assess whether the stability of the particles was still maintainedafter heat treatment.

Again, the particle size was measured using a Malvern Instruments LtdMasterSizer laser diffraction instrument. Measurements were taken priorto milling (0 minutes), during milling (at 10 minutes and 20 minutes)and after milling (at 30 minutes).

Milling time 0 min 10 min 20 min 30 min d(v, 0.1) μm 2.64 2.96 2.34 2.30d(v, 0.5) μm 6.64 7.46 6.01 5.78 d(4, 3) μm 8.03 8.85 6.95 6.65 d(v,0.9) μm 14.70 16.02 11.85 11.32 Modal particle size μm 7.92 9.16 7.056.94

It can be seen that the particles remain very stable under high shearforces even after heat treatment.

High shear mixing stability is important of a predictor of robustnessand would indicate good resistance to mechanical stresses, includingcompressive forces such as those within catalyst installations. Thisrobustness may, for example, be important in end uses relating tocatalysis, and especially where extrusion of is required in themanufacture of the catalyst product, such as in SCR and combinedSCR/DPF.

Example 9

Blaine data, comparing toroidal particles obtained by the invention andspherical particles obtained by the invention, was obtained by a testcarried out according to BS4359: Part 2: 1982.

Both samples were obtained from example 7.

The toroidal sample was one that had been spray dried at a concentrationof 10% wt/wt solids and spray dried at 250° C. (i.e. the product shownin FIG. 6d ).

The spherical sample was one that had spray dried at a concentration of10% wt/wt solids and spray dried at 110° C. (i.e. the product shown inFIG. 6a ).

Sample Toroidal Spherical Blaine Porosity 0.720 0.688 Blaine Test -21180 19869 cm²/g SG (Pycnometer) - 3.08 2.98 g/cm³

It can be seen that the toroidal particles obtained by the inventionhave improved porosity as compared to spherical particles obtained bythe invention.

This shows that the process of the invention can be carried out in amanner to ensure that the toroidal shaped particles are obtained whenend applications are envisaged that required good permeability. Thismay, for example, be the case in end uses such as SCR and combinedSCR/DPF.

Example 10

Concentrated titania sol products were obtained by precipitation thatwas carried out in accordance with the method of WO2011/033286. Thesewere obtained via the Blumenfeld method using various drop ratios. Eachhad a 10 minute drop time.

The micelle size of the titania sols were measured by CPS disccentrifuge particle size analyser.

Samples from each product were spray dried using a LabPlant SD-05laboratory spray drier. The specific surface areas of each of the driedsamples were tested using the BET method. The pore size was measuredusing mercury porosimetry, using a Micromeritics AutoPore IVporosimeter.

It was seen in these experiments that by altering the drop ratio, themicelle size can be controlled and in turn the pore size can becontrolled. In this regard, as the drop ratio was raised from 70:30 uptowards 90:10 the micelle size increased, the pore size increased, andthe surface area decreased.

Drop Ratio 90:10 70:30 Micelle size (nm) 56.7 22.1 Pore Size (nm) 23.43.6 SSA (m2/g) 170.1 295.1

The results set out in the above table clearly illustrate that alteringthe drop ratio has a significant effect:changing the drop ratio from90:10 to 70:30 decreases the micelle size by a factor of over 2.5, andthus gives rise to significantly smaller pore sizes and therefore largerspecific surface area values.

Accordingly, a desired set of properties in the end product can beobtained by suitable control of the parameters in the process ofmanufacture of the titania. For example, if smaller pore sizes (and ahigher SSA) is desired in the product, a lower drop ratio can beselected.

The invention claimed is:
 1. A process for the production of titaniaparticles, the process comprising: providing a titania sol; and dryingthe titania sol to provide dried titania particles, wherein, amorphology of the dried titania particles is controlled by applying oneor more of the following criteria: (a) the titania sol is produced froma TiO₂ containing slurry obtained using a precipitation step in asulphate process, wherein the size of micelles formed during theprecipitation is controlled, (b) the titania sol is produced from a TiO₂containing slurry using a precipitation step in a sulphate process, andthe iso-electric point of the titania is adjusted in order to affect theextent to which the titania sol is flocculated, (c) the titania sol isproduced from a TiO₂ containing slurry using a precipitation step in asulphate process, and the titania sol is dried by application of heatand the temperature used during the drying step is controlled, andwherein, the size of micelles formed during the precipitation iscontrolled by the use of (a) a Mecklenburg precipitation with anucleation level in the range of from 0.1 to 15 wt %, or (b) aBlumenfeld precipitation with a drop ratio of from 50:50 to 99:1.
 2. Theprocess of claim 1, wherein the pore size of the dried titania particlesis controlled by applying one or more of the following criteria: (A-i)the titania sol is produced from a TiO₂ containing slurry obtained usinga precipitation step in a sulphate process, and the size of micellesformed during the precipitation is controlled, (A-ii) the titania sol isproduced from a TiO₂ containing slurry and the iso-electric point of thetitania is adjusted in order to affect the extent to which the titaniasol is flocculated.
 3. The process of claim 1, wherein the shape of thedried titania particles is controlled by applying the followingcriteria: (B-i) the titania sol is dried by application of heat and thetemperature used during the drying step is controlled.
 4. The process ofclaim 1, wherein two or more of the criteria (a) to (c) are applied. 5.The process of claim 1, wherein all three of the criteria (a) to (c) areapplied.
 6. The process of claim 1, wherein all three of the criteria(a) to (c) are applied and the morphology of the dried titania particlesis further controlled by also applying the following criteria: (d) thetitania sol is produced from a TiO₂ containing slurry and the pH of theslurry is controlled in order to affect the extent to which the titaniasol is flocculated.
 7. The process of claim 1, wherein one or moreactive catalytic components are incorporated during the production ofthe titania particles.
 8. The process of claim 1, wherein one or morethermal stabilizer components are incorporated during the production ofthe titania particles.
 9. A process for the production of titaniaparticles, wherein the process comprises: providing a titania sol; andspray drying the titania sol to provide dried titania particles,wherein, a morphology of the dried titania particles is controlled by:producing the titania sol from a TiO₂ containing slurry obtained using aprecipitation step in a sulphate process and adjusting the iso-electricpoint to be 3 pH units or more from the pH of the slurry, by theaddition of dispersant, in order to reduce the extent to which thetitania sol is flocculated, and wherein, a size of micelles formedduring the precipitation is controlled by the use of (a) a Mecklenburgprecipitation with a nucleation level in the range of from 0.1 to 15 wt%, or (b) a Blumenfeld precipitation with a drop ratio of from 50:50 to99:1.
 10. The process of claim 9, wherein the iso-electric point of thetitania is adjusted to be 4 pH units or more from the pH of the slurryby the addition of dispersant, in order to reduce the extent to whichthe titania sol is flocculated.
 11. The process of claim 9, wherein themorphology of the dried titania particles is further controlled by thetemperature used during the spray drying step being controlled.